Drive shafts

ABSTRACT

A drive shaft including an inner shaft having a first end that is adapted to be connectable to a first connecting shaft that is rotated by torque applied by an external electrical machine, and a second end that is adapted to be connectable to a second connecting shaft. A hollow outer shaft, coaxial with the inner shaft, defines at least part of a rotor assembly of an associated electrical machine. The outer shaft is adapted to be releasably connected to the inner shaft so that the drive shaft is selectively configurable in a first arrangement for normal operating conditions where the outer shaft is connected to the inner shaft for rotation therewith, and a second arrangement where the outer shaft is not connected to the inner shaft.

FIELD OF THE INVENTION

Embodiments of the present invention relate to drive shafts, and inparticular to drive shafts for applications where two electricalmachines (e.g., electric motors) are used to drive a single drive shaft.

The drive shafts can be used in marine or ship propulsion assemblies.

BACKGROUND ART

It is not unusual for two electrical machines (e.g., electric motors) tobe arranged to apply torque to a single drive shaft. The electricalmachines are typically arranged in a twin or tandem configuration. Afault in one of the electrical machines will typically mean that thedrive shaft cannot be used until the fault is cleared.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a drive shaft, with twodriving electrical machines, where an electrical machine, such as theelectrical machine that is closest to the load, can be disconnectedeasily, when faulty, so that the drive shaft can be returned to serviceand driven by the remaining electrical machine.

In particular, embodiments of the present invention provide a driveshaft comprising: an inner shaft having: a first end that is adapted tobe connectable to a first connecting shaft that is rotated by torqueapplied by an external electrical machine (e.g., an electric motor); asecond end that is adapted to be connectable to a second connectingshaft; and a hollow outer shaft, coaxial with the inner shaft, the outershaft defining at least part of, or being operatively coupled to, arotor assembly of an associated electrical machine (e.g., an electricmotor that is part of a drive assembly), and being adapted to bereleasably connected to the inner shaft so that the drive shaft isselectively configurable in a first arrangement for normal operatingconditions where the outer shaft is connected to the inner shaft forrotation therewith, and a second arrangement where the outer shaft isnot connected to the inner shaft.

It will be readily appreciated that the first and second connectingshafts do not form part of the drive shaft per se but that the ends ofthe drive shaft are connected to the first and second connecting shaftsin use. The second connecting shaft can be directly or indirectlycoupled to any suitable load, e.g., a propulsion means such as apropeller, impeller, water jet etc. in the case of a marine propulsionassembly. Similarly, the external electrical machine and the non-relatedparts of the associated electrical machine (e.g., the stator assembly,active parts of the rotor assembly etc.) do not form part of the driveshaft per se but can apply a torque to the drive shaft in use. Theelectrical machines can have any suitable construction and can bearranged in a twin or tandem configuration. The outer shaft of the driveshaft can carry the active parts of the rotor assembly of the associatedelectrical machine or can be directly or indirectly coupled to the rotorassembly. In general terms, the external electrical machine will beoperated to apply torque to the inner shaft through the first connectingshaft to which it can be directly or indirectly coupled. The associatedelectrical machine will be operated to apply torque to the outer shaft.

The inner shaft can be rated to take a higher torque than that deliveredby the associated electrical machine.

The first end of the inner shaft can include a connecting flange that isconnectable to a corresponding connecting flange of the first connectingshaft. Similarly, the second end of the inner shaft can include aconnecting flange that is connectable to a corresponding connectingflange of the second connecting shaft. The first and second connectingshafts are therefore connected to the first and second ends of the innershaft in use for rotation therewith. The connecting flange at the secondend of the inner shaft can be releasably connected to the inner shaft.This allows the connecting flange to be fitted to the inner shaft afterit has been properly located within the outer shaft. The respectiveconnecting flanges can be connected together using mechanical fixingssuch as bolts, pins, clamps etc.

The inner shaft can include a first intermediate flange that isreleasably connected to a flange provided at a first end of the outershaft, e.g., using mechanical fixings such as bolts, pins, clamps etc.that can be removed to disconnect the inner and outer shafts at thefirst end and configure the drive shaft in the second arrangement. Inone arrangement, the mechanical fixings are expanding hydraulic bolts.The drive shaft can further comprise a spacer between the firstintermediate flange and the first end flange of the outer shaft. Anysuitable spacer can be used. In one arrangement the spacer can be asegmented ring spacer that is divided into two or more segments, eachsegment receiving at least one mechanical fixing such as a bolt. Such aspacer can be removed in a radial direction while the inner shaftremains in place.

To provide additional protection against high shock loading, the innerand outer shafts can be releasably connected at both ends of the outershaft. In particular, the inner shaft can further include a secondintermediate flange that is releasably connected to a flange provided ata second end of the outer shaft, e.g., using mechanical fixings such asbolts, pins, clamps etc. that can be removed to disconnect the inner andouter shafts at the second end and configure the drive shaft in thesecond arrangement. The drive shaft can further comprise a spacerbetween the second intermediate flange and the second end flange of theouter shaft. Once again, any suitable spacer can be used, e.g., asegmented ring spacer. Each spacer between an intermediate flange andthe adjacent end flange of the outer shaft can be removed when the innerand outer shafts are disconnected to allow a clear gap to be createdbetween the respective flanges.

In general terms, it will be readily appreciated that any suitable meanscan be used to releasably connect the inner and outer shafts to enablethe drive shaft to be selectively configurable in the first or secondarrangement. Such means can be provided at one or both ends of the outershaft. The means can be a coupling of any suitable type (e.g., flange,viscous, magnetic, flexible etc.) or a clutch assembly of any suitabletype (e.g., dog, friction, magnetic etc.). It will be readilyappreciated that such means do not necessarily need to use correspondingflanges on the inner and outer shafts. The inner and outer shafts can bephysically adapted or constructed in other ways to facilitate theirreleasable connection.

During normal operating conditions, torque from the external electricalmachine can be transmitted between the first and second connectingshafts through the inner shaft. Torque from the associated electricalmachine can also be transmitted between the outer shaft and the innershaft through the intermediate flange(s). In the case of a faultcondition which prevents the outer shaft from being rotated, the innerand outer shafts can be disconnected (e.g., by removing the bolts, pins,claims or other mechanical fixings, or by operating the clutch assembly)so that torque can still be transmitted between the first and secondconnecting shafts through the inner shaft. This means that the driveshaft can still be used even if there is a fault that requires the outershaft to remain stationary.

In an embodiment, the connecting flanges and intermediate flanges of theinner shaft are located axially outside the outer shaft.

The outer shaft can further comprise one or more collars to preventlateral movement of the drive shaft. Such collars are not normallyintended to bear thrust load.

An embodiment of the present invention further provides a drive assemblycomprising: a drive shaft as herein described; and an associatedelectrical machine having a rotor assembly defined at least in part by,or operatively coupled to, the outer shaft.

The drive assembly can further comprise one or more bearings forsupporting the drive shaft.

The drive assembly can further comprise locking means for selectivelypreventing rotation of the outer shaft when the drive shaft is in thesecond arrangement.

The drive shaft (or the drive assembly) can be part of a marinepropulsion assembly where the second connecting shaft can be used todrive propulsion means, e.g., a propeller, impeller, water jet etc. Amarine propulsion assembly can also include components such as one ormore plummer blocks, thrust block etc.

An embodiment of the present invention further provides a method ofoperating a drive shaft comprising: an inner shaft having: a first endthat is adapted to be connectable to a first connecting shaft that isrotated by torque applied by an external electrical machine; a secondend that is adapted to be connectable to a second connecting shaft; anda hollow outer shaft, coaxial with the inner shaft, the outer shaftdefining at least part of, or being operatively coupled to, a rotorassembly of an associated electrical machine, and being adapted to bereleasably connected to the inner shaft; the method comprising the stepsof: connecting the outer shaft to the inner shaft during normaloperating conditions; and disconnecting the outer shaft from the innershaft in response to a fault condition.

If the inner shaft includes a first intermediate flange that isreleasably connected to a flange provided at a first end of the outershaft using mechanical fixings such as bolts, pins, clamps etc. themethod can include the step of removing the mechanical fixings todisconnect the outer shaft from the inner shaft in response to a faultcondition. If the drive shaft includes a clutch assembly, the method caninclude the step of operating the clutch assembly to disconnect theouter shaft from the inner shaft in response to a fault condition.

The method can further include the step of preventing rotation of theouter shaft when disconnected from the inner shaft.

DRAWINGS

FIG. 1 shows a drive assembly incorporating a first drive shaftaccording to an embodiment of the present invention;

FIG. 2 shows a drive assembly incorporating a second drive shaftaccording to an embodiment of the present invention;

FIG. 3 is a schematic view of a marine propulsion assembly incorporatinga drive shaft according to an embodiment of the present invention; and

FIG. 4 is a schematic view of the marine propulsion assembly of FIG. 3where the associated electric motor is out of service.

DETAILED DESCRIPTION

With reference to FIG. 1, a drive assembly 1 for a marine propulsionassembly includes a first drive shaft 2 according to an embodiment ofthe present invention. It will be readily appreciated that the driveassembly 1 is not limited to marine applications and can be used forother purposes.

The drive shaft 2 includes an inner shaft 4 and a hollow outer shaft 6that is coaxially located with respect to the inner shaft and spacedapart by an axial gap 8.

The inner shaft 4 has a first end 4 a and a second end 4 b. The firstend 4 a includes a connecting flange 10 that is connected to aconnecting flange 12 of a first connecting shaft 14 by means of a seriesof circumferentially spaced bolts 16. The second end 4 b includes aconnecting flange 18 that is connected to a connecting flange 20 of asecond connecting shaft 22 by means of a series of circumferentiallyspaced bolts 24. The connecting flange 18 can be fitted to the secondend 4 b after the inner shaft 4 has been inserted through the outershaft 6.

The outer shaft 6 includes a first end 6 a and a second end 6 b.

The inner shaft 4 includes an intermediate flange 26 that is releasablyconnected to an end flange 28 at the first end 6 a of the outer shaft 6by means of a series of circumferentially spaced bolts 30, e.g.,expanding hydraulic bolts. Although not shown, it will be readilyappreciated that the inner and outer shafts 4, 6 can be releasablyconnected together by other types of mechanical fixing or by a clutchassembly.

A segmented ring spacer 32 is located between the intermediate flange 26and the end flange 28. As described above, the spacer 32 is divided intotwo or more segments and each segment receives one or more of the bolts32 so that they are retained in position between the flanges 26, 28.

The outer shaft 6 includes a pair of axially spaced collars 34 thatprevent lateral movement. Each collar 34 is positioned adjacent abearing 36 that supports the drive shaft 2.

An associated electric motor 38 (or ‘aft motor’) includes a rotorassembly 40 that is provided on the outer shaft 6.

During normal operation, the intermediate flange 26 and the end flange28 are connected by the bolts 30.

Torque is provided by an external electric motor (not shown) to thefirst connecting shaft 14 and is transmitted to the second connectingshaft 22 by the inner shaft 4. Torque provided by the associatedelectric motor 38 is transmitted to the second connecting shaft 22 bythe outer shaft 6 and the inner shaft 4 through the intermediate flange26 and the end flange 28.

In the event of a fault where the outer shaft 6 cannot rotate, the bolts30 can be manually removed to disconnect the intermediate flange 26 andthe end flange 28, and hence disconnect the stationary inner and outershafts 4, 6. The segmented ring spacer 32 is also removed to provide aclear gap between the intermediate flange 26 and the end flange 28. Theouter shaft 6 can optionally be locked to prevent rotation by a lockingmeans (not shown).

The inner shaft 4 is still capable of transmitting torque from theexternal electric motor (not shown) to the second connecting shaft 22.No torque is applied to the outer shaft 6 by the inner shaft 4 during afault condition.

When the fault condition has been cleared, the inner shaft can be heldstationary while the segmented ring spacer 32 is repositioned betweenthe intermediate flange 26 and the end flange 28 and the bolts 30 aremanually reinserted to reconnect the intermediate flange 26 and the endflange 28.

FIG. 2 shows a drive assembly 1′ that includes a second drive shaft 2′according to the present invention. The second drive shaft 2′ is similarto the first drive shaft shown in FIG. 1 and like components have beengiven the same reference numbers.

The second drive shaft 2′ provides additional protection in situationswhere the associated electric motor 38 is subject to high shock loading.The inner shaft 4′ includes a first intermediate flange 26 a that isreleasably connected to an end flange 28 a at the first end 6 a of theouter shaft 6′ by means of a series of circumferentially spaced bolts 30a. The inner shaft 4′ also includes a second intermediate flange 26 bthat is releasably connected to an end flange 28 b at the second end 6 bof the outer shaft 6′ by means of a series of circumferentially spacedbolts 30 b. The second intermediate flange 26 b can be fitted to theinner shaft 4′ after it has been inserted through the outer shaft 6′. Asegmented ring spacer 32 a is located between the intermediate flange 26a and the end flange 28 a. Similarly, a segmented ring spacer 32 b islocated between the intermediate flange 26 b and the end flange 28 b. Inthe configuration shown in FIG. 2, i.e., during normal operation, thesecond drive shaft 2′ is capable of withstanding high shock loads.

In the event of a fault where the outer shaft 6′ cannot rotate, thebolts 30 a can be removed to disconnect the intermediate flange 26 a andthe end flange 28 a, and the bolts 30 b can be removed to disconnect theintermediate flange 26 b and the end flange 28 b. The segmented ringspacers 32 a, 32 b are also removed to provide a clear gap between therespective intermediate flange and the end flange.

When the fault condition has been cleared, the inner shaft can be heldstationary while the segmented ring spacers 32 a, 32 b are repositionedbetween the respective intermediate and end flanges 26 a, 28 a and 26 b,28 b. The bolts 30 a are then manually reinserted to reconnect theintermediate flange 26 a and the end flange 28 a and the bolts 30 b aremanually reinserted to reconnect the intermediate flange 26 b and theend flange 28 b.

With reference to FIGS. 3 and 4, a marine propulsion assembly 100includes a drive assembly 1 as described above with reference to FIG. 1.

The first connecting shaft 14 passes through a bulkhead seal 102 in awatertight bulkhead 104 and is connected to an electric motor 106 (or‘forward motor’).

The second connecting shaft 22 is connected to a propeller 108 by meansof a first plummer block 110, a thrust block 112 and a second plummerblock 114. A stern seal 116 is provided in the hull 118 of the marinevessel.

FIG. 3 shows the drive assembly during normal operating conditions.

FIG. 4 shows the drive assembly during a fault condition where theelectric motor 38 is out of service. In particular, the bolts 30 and thesegmented ring spacer 32 have been removed so the outer shaft 6 isdisconnected from the inner shaft 4.

The inner shaft 4 is still capable of transmitting torque from theelectric motor 106 to the second connecting shaft 22 to rotate thepropeller 108.

The shaft that supports the rotor assembly of the electric motor 106 isconnected to the first connecting shaft 14. The first connecting shaft14 can be formed as two intermediate shaft sections 14 a, 14 b that canbe disconnected from each other in a similar manner to that discussedabove. If there is a fault condition where the electric motor 106 is outof service, it can be disconnected from the drive assembly 1. Inparticular, the support shaft can be disconnected from the first shaftsection 14 a (which can also optionally be removed completely) and thesecond shaft section 14 b can be disconnected from the first end 4 a ofthe inner shaft. The second shaft section 14 b passes through thebulkhead seal 102 and can be supported on a temporary cradle.

The electric motor 38 can still be operated and torque is transmitted tothe second connecting shaft 22 by means of the outer shaft 6 and theinner shaft 4 to rotate the propeller 108.

This written description uses examples to disclose the invention,including the preferred embodiments, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. A drive shaft comprising: an inner shaftcomprising: a first end configured to be connectable to a firstconnecting shaft that is rotated by torque applied by an externalelectrical machine; and a second end configured to be connectable to asecond connecting shaft; and a hollow outer shaft, coaxial with theinner shaft, the outer shaft defining at least part of, or beingoperatively coupled to, a rotor assembly of an associated electricalmachine, and being configured to be releasably connected to the innershaft so that the drive shaft is selectively configurable in a firstarrangement for normal operating conditions where the outer shaft isconnected to the inner shaft for rotation therewith, and a secondarrangement where the outer shaft is not connected to the inner shaft.2. The drive shaft according to claim 1, wherein the inner shaft furthercomprises a first intermediate flange releasably connected to a flangeprovided at a first end of the outer shaft.
 3. The drive shaft accordingto claim 2, further comprising a spacer between the first intermediateflange and a first end flange of the outer shaft.
 4. The drive shaftaccording to claim 2, wherein the inner shaft further comprises a secondintermediate flange releasably connected to a flange provided at asecond end of the outer shaft.
 5. The drive shaft according to claim 4,further comprising a spacer between the second intermediate flange and asecond end flange of the outer shaft.
 6. The drive shaft according toclaim 5, further comprising a spacer between the first intermediateflange and a first end flange of the outer shaft.
 7. The drive shaftaccording to claim 1, wherein the inner and outer shafts are releasablyconnected using mechanical fixings that can be removed to configure thedrive shaft in the second arrangement.
 8. The drive shaft according toclaim 2, wherein the inner and outer shafts are releasably connectedusing mechanical fixings that can be removed to configure the driveshaft in the second arrangement.
 9. The drive shaft according to claim4, wherein the inner and outer shafts are releasably connected usingmechanical fixings that can be removed to configure the drive shaft inthe second arrangement.
 10. The drive shaft according to claim 1,wherein the inner and outer shafts are releasably connected using aclutch assembly.
 11. The drive shaft according to claim 7, wherein theinner and outer shafts are releasably connected using a clutch assembly.12. The drive shaft according to claim 1, wherein the outer shaftfurther comprises one or more collars to prevent lateral movement of thedrive shaft.
 13. The drive shaft according to claim 11, wherein theouter shaft further comprises one or more collars to prevent lateralmovement of the drive shaft.
 14. A drive assembly, comprising a driveshaft comprising: an inner shaft comprising: a first end configured tobe connectable to a first connecting shaft that is rotated by torqueapplied by an external electrical machine; and a second end configuredto be connectable to a second connecting shaft; and a hollow outershaft, coaxial with the inner shaft, the outer shaft defining at leastpart of, or being operatively coupled to a rotor assembly, and beingconfigured to be releasably connected to the inner shaft so that thedrive shaft is selectively configurable in a first arrangement fornormal operating conditions where the outer shaft is connected to theinner shaft for rotation therewith, and a second arrangement where theouter shaft is not connected to the inner shaft; and an electricalmachine comprising the rotor assembly.
 15. The drive assembly accordingto claim 14, further comprising one or more bearings for supporting thedrive shaft.
 16. The drive assembly according to claim 14, furthercomprising a lock configured to selectively prevent rotation of theouter shaft when the drive shaft is in the second arrangement.
 17. Amarine propulsion assembly comprising a drive shaft according to claim1, wherein the second connecting shaft is used to drive a propulsion.18. A method of operating a drive shaft, wherein the drive shaftincludes an inner shaft having a first end configured to be connectableto a first connecting shaft that is rotated by torque applied by anexternal electrical machine, and a second end configured to beconnectable to a second connecting shaft, and a hollow outer shaft,coaxial with the inner shaft, the outer shaft defining at least part of,or being operatively coupled to, a rotor assembly of an associatedelectrical machine, and being configured to be releasably connected tothe inner shaft, the method comprising: connecting the outer shaft tothe inner shaft during normal operating conditions; and disconnectingthe outer shaft from the inner shaft in response to a fault condition.19. The method according to claim 18, wherein the inner and outer shaftsare releasably connected by mechanical fixings or a clutch assembly, themethod further comprising: removing the mechanical fixings or operatingthe clutch assembly to disconnect the outer shaft from the inner shaftin response to a fault condition.
 20. The method according to claim 18,further comprising preventing rotation of the outer shaft whendisconnected from the inner shaft.